The invention relates to release compositions useful in release layers of release articles (e.g., release liners) and adhesive articles (e.g., pressure sensitive adhesive tapes (PSA)).
Polymeric release materials are known to be used in release layers in release articles (e.g., release liners) and adhesive articles (e.g., adhesive tapes) in order to provide a surface from which an adhesive can be easily and cleanly removed. For example, it is known to apply a polymeric release material to the back surface of an adhesive tape (e.g., masking tape) in order to allow the tape to be provided in roll form and to be easily and conveniently dispensed by unwinding the roll. The release coating is expected to reproducibly provide an appropriate unwind force throughout the lifetime of the tape roll, and to not deleteriously affect the adhesive.
The Handbook of Pressure Sensitive Adhesive Technology, 2nd Ed., D. Sat as Ed., Van Nostrand Reinhold, N.Y., 1989, Chapter 23, describes polymers which may be used as release agents for PSA tapes. Various polymers of lower critical surface tension such as silicones, fluorine containing polymers, and long alkyl side chain polymers are useful as release coatings. Long alkyl side chain polymers generally contain 16-20 carbon atoms in the alkyl side chains, and can be used to prepare release coatings that provide medium release forces which are especially desirable for PSA tapes. For example, GB 870,022 describes the use of copolymers prepared from octadecyl acrylate, acrylonitrile, acrylic acid, and methyl acrylate for tape release coatings.
The use of polymers or copolymers containing fluoroalkyl side groups has also been disclosed (U.S. Pat. No. 3,318,852). It has been found that the perfluoroalkyl groups need to contain at least 6 carbon atoms, and preferably at least 8 carbon atoms, in order for the polymer to provide sufficiently low unwind forces for tape rolls. However, it has been reported that certain perfluorooctyl-containing compounds may tend to bioacummulate in living organisms, raising concerns about their use. Recently, it has been found that perfluorobutyl-containing compounds are eliminated from the body much more effectively.
In the case of masking tapes, the release coating is expected to provide moderate unwind force, between about 10-40 N/dm. If the unwind force is too low, the tape roll may inadvertently unwind under its own weight, and if the unwind force is too high, the tape roll will be difficult to unwind. In addition, the unwind force should be relatively stable over the lifetime of the roll. Another common requirement for masking tapes is that the release coating on the tape backside should provide good wetting and anchorage of both water and solvent based paints. Poor paint wetting and anchorage can result in paint flaking when the masking tape is removed from the substrate, thereby ruining the appearance of the freshly painted surface. Still another common requirement for masking tapes is that they have good holding power to their own backing. For example, in a paint-draping situation, one piece of masking tape may be used to attach a drape onto another piece of masking tape, that is, overtaping, that had been placed onto the surface to establish a paint line. Typically, improving one of these masking tape property requirements can result in a deterioration of another property. For example, in the case of a more aggressive PSA, a release coating that can provide easier and more stable release must be employed; however, such release coatings may not provide good paint wetting/anchorage or sufficient holding power to backing. In such cases, a compromise in overall release coating performance features must be reached.
One commonly used method of forming a release layer is to coat the release material from an organic solvent-based solution onto a substrate. After the solution has been applied to the substrate, the solvent is evaporated leaving behind a relatively uniform coating of the release material. As environmental regulations tighten, release materials that can be processed using organic solvent-free processes are more desirable.